Recently a set of Swedish male monozygotic triplets was reported, all diagnosed as schizophrenic, characterized by numerous clinical and anatomical similarities. A cytogenetic study showed that, in addition, all the men and their father had an extra band at chromosome 15p containing repetitive DNA with an as yet unknown effect on the phenotype (Jonsson et al., 1997). To test whether the extra chromosomal band at 15p may be a marker for excess multiple schizophrenic birth, we investigated blood samples obtained on two different occasions from the Genain quadruplets (when they were 66 years of age), as well as a sample from the adult son of one of the quadruplets. We used high resolution chromosomal analysis (Johannesson et al., 1991), including C-banding (Sumner 1972). The karyotypes were examined independently by two cytogeneticists. All karyotypes were within normal limits and no extra band on chromosome 15 was evident. We conclude that the abnormality at chromosome15p in the Swedish triplets was not shared by another set of multiple, genetically-identical siblings with schizophrenia. The present result indicates that the importance, if any, of the extra band on chromosome 15p in the Swedish triplets is not related to excess development of schizophrenia among multiple monozygotic births.